Kryptonite

An element from the planet Krypton that only exists in small chunks. It currently is one of the few elements that can pose as a harmful substance to Superman. If he comes into contact with him, his steroid - based powers weaken.

To make matters worse, the element Krypton, presumably a component of Kryptonite if it were a compound, is an inert gas that does not form compounds under ordinary conditions. Superman's anathema is an imaginary compound masquerading as an element.